There are quite a few sources on the Internet about cultivating cacti and other succulents. The most comprehensive and, for beginners, suitable ones are the Cactus Cultivation Notes. There are written for the USA but also quite suitable for South Africa.
But first a few important notes: If anyone tells you that “cacti grow virtually anywhere in South Africa”; just forget about that. Better is to say that there is a cactus for virtually every place in South Africa. The same applies for (indigenous) succulents. Ernst van Jaarsveld of Kirstenbosch Botanical Gardens in Cape Town was very right last year in his weekly column in one of the newspapers that 60 to 70 percent of the succulents, including cacti, sold to people in the Cape Town area die within months or suffer. This is also the reason that we sometimes refuse to sell plants if we find out that the local environment of the plants is not in line with certain plant-specific requirements. In the future we will come back to this subject in other contributions.
But first some general info. It all starts with good soil with free drainage. We have two main general mixtures for our nursery. One for succulents and one for cacti and cactuslike Euphorbia’s for the latter ones are retaining more water than succulents. And we have special mixtures for specific plant-groups like the Lithops but that is something for later.
1) succulent soil mix: 4 parts coarse river sand, 3 parts clayish loam and one part compost.
2) Cacti and Euphorbia: 6 parts coarse river sand, 1 part clayish loam and one part compost.
Another generalisation: succulents prefer alkaline ( ph 7 - 8 ) soil but there are a few exceptions. We’ll come back on that in the future.
A good, natural, way of preventing soil and climate (wet) related diseases is to make a tea of khakibush (Tagetes minuta) which is indigenous to Southern Africa. Fill a bucket with this weed, pour boiled water over it and let it stand for at least 24 hrs. Smelly but very effective. Moisterize the soil-mix with the tea. That’s all. In the garden: sow seed of Khakibush and, just before it start to flower, dig it into the soil. It’s a bit more time consuming than but surely as effective as chemicals like Temmex and Dithane which most of the nurseries are applying to their soil to prevent succulents from rot related diseases.
Planting (repotting) cacti and aloes: Cut back the roots and let the plants dry for a couple of days. For euphorbias: when cutting the roots (which we do NOT advise but sometimes it seems a necessity) be aware of latex dripping out of the wounds. Keep the roots under the water tap until latex stops dripping. This milky sap is poisonous (as is sap of many plants) and it is advisable to wash your hands thoroughly afterwards!
Planting in the open (especially cacti and eurphorbias): For columnar ones we strongly recommend to surround them with large rocks; i.e. make the plant hole wide enough, cover the roots with a layer of soil, surround the plants with large rocks and fill the gap between plant and rocks with coarse sand. This precaution prevents uprooting by natural causes such as in windy environments. For all cacti and euphorbias it’s wise to plant them on a small heep of 5 to 10 cm above ground-level. This is also a good way to prevent neck-rot in especially Winter rainfall areas. Once the plant is established after one or two years the ‘heep’ will have equalised itself with the surrounding.
Once potted or planted in the open do not water the plants for the first days or even a few weeks although one cannot prevent rain.
Some succulents prefer full sun and some shade. Just look in the ‘veld’: Gasterias and Haworthias are normally growing in the shade of a bush. You can simulate that by planting these shade-loving plants in, for example, the shade of a tree or rock. These plants will also grow in full sun but especially during the Summer you can see the difference in leaf colour.
In general (specially Cape Town area): most succulents like to grow on a North facing slope. Although there are exceptions we always advise customers in the more moist areas (f.e. Simonstown, Kommetjie, Houtbay) to keep succulents in pots. Deep pots for columnar growing succulents and wide ones for barrelshape cacti and low growing succulents. Small aloes in relativily wide post and tree like aloes in relativily deep pots.